Atherosclerosis, a process in which the walls of the arteries thicken due to the accumulation of plaque in the blood vessels, is the cause of most coronary artery disease (CAD) that can result in heart attacks, strokes, or inadequate circulation to the extremities. Arterial occlusions caused by plaque accumulation may necessitate major invasive surgery, such as a coronary by-pass procedure. However, less invasive, percutaneous methods may be an alternative in treating atherosclerosis. For example, percutaneous transluminal coronary angioplasty (PTCA) involves advancing a balloon catheter through a body lumen to a target treatment site. In one example, a small incision is made near the femoral artery to insert the catheter, which is then advanced to a plaque area in the coronary artery. The catheter has a deflated balloon near a distal end, and the balloon is positioned across the plaque. Once in position, the balloon is inflated to crack or flatten the plaque, thereby restoring the normal patency of the blood vessel. The balloon is then deflated so that the catheter can be removed, allowing blood flow to resume through the dilated blood vessel.
Percutaneous delivery of therapeutic agents may also be performed alone or in combination with PCTA treatments. Needle catheters are one type of percutaneous medical devices that may be used to deliver a therapeutic agent or drug to treat diseases associated with CAD. However, the tortuous nature of vessels in the body make it difficult for advancing a needle catheter to a target treatment site. Furthermore, to optimize a therapeutic drug treatment, the active drug or biologic agent may need to be injected directly into a vessel wall. This type of drug delivery requires a high level of accuracy because the proper point in the vessel wall should be penetrated. In another type of drug delivery treatment with a needle catheter, biologically active agents may be delivered to a cardiac structure (such as into an intraventricular wall), which also requires that the needle catheter be flexible enough to navigate and advance through body vessels and to the heart. U.S. Pat. No. 6,093,177 describes one type of flexible catheter that may be used within a heart chamber.
FIG. 1 illustrates an example of a prior art needle catheter. The needle tip is connected to a needle shaft that may be steered and moved from a retracted position within a sleeve and an extended position past a distal end of the sleeve to penetrate a body tissue. The needle shaft may have a tubular lumen so that a drug or biologic agent may be injected through the needle tip to the body tissue. The needle tip (along with the needle shaft) is usually a continuous piece of metallic material to provide sufficient strength and support to prevent kinking during advancement through a tortuous vessel and tissue penetration.
One problem with a metallic needle and/or needle shaft is that it may not provide the necessary flexibility to navigate through tortuous body vessels, which are characteristic of arterial regions. Because of the lack of flexibility of these needle catheters, it may be difficult to deliver biologic agents deep within the arterial regions of the body. Moreover, it may be even more difficult to bend the penetrating tip of the needle to pierce a vessel wall to optimize drug delivery treatment.